Hydrolases, zinc enzyme reactions

The normal zinc content of the body amounts to 20-30 mmol (1.3-2.0 g). The daily dietary requirement is 10-15 mg. In the blood, zinc is bound to tt2-macro-globulin, albumin or amino acids, and a small amount is also bound to transferrin. Zinc is crucial to a variety of enzyme reactions. This applies especially to the liver. More and more attention has therefore been paid to the role of zinc in liver disease in recent years. Six enzyme groups (hydrolases, isomerases, ligases, lyases, oxidore-ductases and transferases) with a total of 35 zinc metal-loenzymes are listed. (98) Almost 200 enzyme reactions in the body are zinc-dependent ... 

Zinc is an essential trace element. More than 300 enzymes that require zinc ions for activity are known. Most catalyze hydrolysis reactions, but zinc-containing representatives of aU enzyme classes are known, such as, for instance, alcohol dehydrogenase (an oxidoreductase), famesyl-Zgeranyl transferase (a transferase), -lactamase (a hydrolase), carbonic anhydrase (a lyase) and phosphomannose isomerase. 

Enzymes that contain binuclear metal centers are also well suited to catalyze hydrolysis reactions, including a number of the reactions described above for the mononuclear metallohydrolases. Additionally, several of the examples that are discussed here belong to the enzyme superfamilies described above, specifically the amidohydrolase, zinc a,/3-hydrolase, and metallo-/31 superfamilies. The substrates for the binuclear metallohydrolases are also biologically diverse, including proteins, peptides, nucleotides, polyamines, and xenobiotics. The binuclear nature of these metal centers produces an active site with altered properties compared to the mononuclear counterparts, and therefore catalysis by these enzymes occurs with alternative reaction mechanisms. Readers are referred to the preceding sections for background information pertaining to enzymes that have already been discussed. 

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